The invention relates to a thermal printer, and more particularly to a pressing mechanism between a print head and a platen.
A conventional printer that pressed and retracted its platen includes a unitized mechanism consisting of a motor, an eccentric cam valid for both pressing and releasing directions and an arm. It has a pressuring spring on a thermal head side to press the platen onto a thermal head so that a nip pressure is applied. This system has addressed, e.g., the following problems.
a) When the platen is pressed or retracted, vibrations of the thermal head are caused due to a pressing spring disposed on the thermal head side. As a result, a condition of a printing press section is changed. Specifically, when the ribbon dispenser is used for printing, a sheet having a ribbon thereon travels through a path from the printing press section to the ribbon dispenser. At this time, the path is changed by vibrating the thermal head described above to change a position at which the ribbon separated. Therefore, it is difficult to obtain a satisfactory print quality in stable manner, and a folded portion of the ribbon is undesirably caused. Additionally, the vibrations of thermal head are also generated by adjusting a nip pressure when the thickness or type of sheet is changed.
b) When the head is replaced by a new one, replacing work is difficult owing to the spring pressure applied to the head.